Truck tractor



FIG. 1 is a perspective view of a truck tractor, showing my new design;

FIG. 2 is a right side view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a left side view thereof. 

The ornamental design for a truck tractor, as shown and described. 